can't retrieve the output of jit.str.tosymbol using callback in javascript

I am trying to retrieve a symbol returned by jit.str.tosymbol object within javascript (jit.str.tosymbol is instantiated as JitterObject). However when I call matrixcalc(some_matrix,some_matrix) on jit.str.tosymbol object the callback is called with event.eventname == "attr_modified", and event.args[0] == "outsym".

Below is a test patch and attached is a js file. Any help would be much appreciated.

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